Compositions and methods for planarizing or polishing the surface of a substrate are well known in the art. Chemical-mechanical planarization, or chemical-mechanical polishing (CMP), is a common technique used to planarize substrates. CMP utilizes a chemical composition, known as a CMP composition or more simply as a polishing composition (also referred to as a polishing slurry) for removal of material from the substrate. Polishing compositions typically are applied to a substrate by contacting the surface of the substrate with a polishing pad (e.g., polishing cloth or polishing disk) saturated with the polishing composition. The polishing of the substrate typically is further aided by the chemical activity of the polishing composition and/or the mechanical activity of an abrasive suspended in the polishing composition or incorporated into the polishing pad (e.g., fixed abrasive polishing pad).
Conventional CMP compositions and methods typically are not entirely satisfactory at planarizing substrates. In particular, CMP polishing compositions and methods can result in less than desirable polishing rates and high surface defectivity when applied to a substrate. Because the performance of many substrates is directly associated with the planarity of their surfaces, it is crucial to use a CMP composition and method that results in a high polishing efficiency, selectivity, uniformity, and removal rate and leaves a high quality polish with minimal surface defects.
The difficulty in creating an effective polishing composition for semiconductor wafers stems from the complexity of the semiconductor wafer. Semiconductor wafers are typically composed of a substrate, on which a plurality of transistors has been formed. Integrated circuits are chemically and physically connected into a substrate by patterning regions in the substrate and layers on the substrate. To produce an operable semiconductor wafer and to maximize the yield, performance, and reliability of the wafer, it is desirable to polish select surfaces of the wafer without adversely affecting underlying structures or topography. In fact, various problems in semiconductor fabrication can occur if the process steps are not performed on wafer surfaces that are adequately planarized.
CMP compositions often contain oxidizing agents, which can react with the surface of the substrate and render the surface more susceptible to removal by mechanical abrasion. Oxidizing agents containing hydrogen peroxide have been used for this purpose, but may not provide a satisfactory removal rate for certain substrates, including those which are not highly reactive to peroxide.
Organic polymer materials, for example, have unique chemical and mechanical characteristics that must be addressed during chemical-mechanical polishing, including that they can be mechanically soft and easy to scratch. In contrast to their mechanical sensitivity, however, organic polymers are often chemically inert. The combination of these chemical and mechanical characteristics makes organic polymer dielectric materials difficult to polish using a traditional aqueous based CMP composition. Organic polymer materials typically have a dielectric constant of about 1 or more and include polymers with a relatively high organic content, polymers with a low and high organic content with a high level of porosity, polymers with relatively low organic content based upon silicon-oxygen type materials and inorganic materials, or polymers with a combination of these properties.
Phase change alloys (PCAs) are another example of substrate materials that can be relatively soft, and have unique characteristics that must be addressed during chemical-mechanical polishing. PRAM (Phase Change Access Memory) devices (also known as Ovonic memory devices) use phase change materials (PCMs) that can be electrically switched between an insulating amorphous and conductive crystalline state for electronic memory application. Typical materials suited for these applications utilize various chalcogenide (Group VIB) and Group VB elements of the periodic table (e.g., Te, Po, and Sb) in combination with one or more of In, Ge, Ga, Sn, and Ag, which are referred to as phase change alloys (PCAs). Particularly useful PCAs are germanium (Ge)-antimony (Sb)-tellurium (Te) alloys (GST alloys), such as an alloy having the formula Ge2Sb2Te5. These materials can reversibly change physical states depending on heating/cooling rates, temperatures, and times. Other useful alloys include indium antimonite (InSb). The physical properties of many PCAs, including GST and InSb, make them soft relative to other PCM materials.
A need remains for a polishing composition and polishing methods that will exhibit desirable planarization efficiency, uniformity, and removal rate during the polishing and planarization of substrates such as organic polymer materials and PCAs, while minimizing defectivity, such as surface imperfections and damage to underlying structures and topography during polishing and planarization. The invention provides such a polishing composition and methods. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.